Quinolines and their derivatives are an important class of compounds in medicinal applications and are widely occurred in natural products [(a) Y. Morimoto, F. Matsuda, H. Shirahama, Synlett, 1991,202; (b) M. Isobe, T. Nishikawa, N. Yamamoto, T. Tsukiyama, A. Ino, T. Okita, J. Heterocycl. Chem. 1992, 29, 619; (c) J. P. Michael, Nat. Prod. Rep. 1997, 14, 605] and drugs [(a) D. G. Markees, V. C. Dewey, G. W. Kidder, J. Med. Chem. 1970, 13, 324; (b) A. A. Alhaider, M. A. Abdelkader, E. J. Lien, J. Med. Chem. 1985, 28,1398; (c) S. F. Campbell, J. D. Hardstone, M. J. Palmer, J. Med. Chem. 1988, 31,1031]. Several quinoline derivatives have been found to possess useful biological activities like antibacterial (H. V. Patel, K. V. Vyas, P. S. Fernandes; Indian J. Chem. 1990, 29B, 836.), antimalarial, anti-inflammatory etc. Thus quinoline heterocyclic ring system occupies a pride of place in organic and medicinal chemistry by way of useful biological profiles as mentioned above. Skraup's (H. Skraup, Chem. Ber. 1880, 13, 2086; R. H. F. Mansake, M. Kulka, Org.React. 1953,7,59.) procedure is the classical method for the construction of quinoline nucleus requiring drastic reaction conditions using sulfuric acid as catalyst. Many methods have been reported for the synthesis of quinolines and most of them suffer from drawbacks like use of hazardous and expensive reagents, drastic reaction conditions and poor yields. In another approach quinoline skeleton is prepared by the reaction of aminoarenes and olefins employing transition metal complexes as catalysts [(a) S. E. Diamond, A. Szalkiewicz, F. Mares, J. Am. Chem.
Soc. 1979,101, 490; (b) T. Joh, N. Hagihara, Tetrahedron Lett. 1967, 8, 4199). The quinoline moiety can also be prepared by the reaction of aminoarenes with aliphatic aldehydes under non acidic conditions (Y. Watanabe, S. C. Shim, T. Mitsudo, Bull. Chem. Soc. Jpn.1981, 54, 3460).
Reference may be made to F. N. Campbell, I. J. Scchaffner, J. A. C. S., 1995, 67, 86-89; M. A. Clapp, R. S. Yipson, J. A. C. S., 1946, 68,1332-34; J. Spencer, M. Pfeffer, Tetrahedron Asymmetry, 1995, 6(2),419-426.
All the existing methods for the preparation of quinoline ring skeleton have the following disadvantages.                1. Use of hazardous chemicals like concentrated sulfuric acid, which is corrosive and produce waste at the source, requiring effluent treatment, and have negative influence on the economy.        2. It is inconvenient to handle concentrated sulfuric acid in large-scale synthesis.        3. Drastic reaction conditions i.e. carrying out the reaction at high temperatures.        4. Use of expensive transition metal complexes thereby polluting the environment.        5. Purification of the product using column chromatography or preparative thin layer chromatography is not economical on large-scale process, since the yield of the product will be reduced.        6. Significant yield variations with variant substituents on phenyl ring.        